The present invention relates to an improved process for producing alkylaromatics such as ethylbenzene and cumene.
Of the alkylaromatic compounds advantageously produced by the present improved process, ethylbenzene and cumene, for example, are valuable commodity chemicals which are used industrially for the production of styrene monomer and coproduction of phenol and acetone respectively. In fact, a common route for the production of phenol comprises a process which involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide, and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone. Ethylbenzene may be produced by a number of different chemical processes. One process which has achieved a significant degree of commercial success is vapor phase alkylation of benzene with ethylene in the presence of a solid, acidic ZSM-5 zeolite catalyst. Examples of such ethylbenzene production processes are described in U.S. Pat. No. 3,751,504 (Keown), U.S. Pat. No. 4,547,605 (Kresge) and U.S. Pat. No. 4,016,218 (Haag). U.S. Pat. No. 5,003,119 (Sardina) describes the use of zeolite X, zeolite Y, zeolite L, zeolite Beta, ZSM-5, zeolite Omega, and mordenite and chabazite in synthesis of ethylbenzene. U.S. Pat. No. 5,959,168 (van der Aalst) describes the use of zeolite Y, zeolite Beta, MCM-22, MCM-36, MCM-49 and MCM-56 in synthesis of ethylbenzene in a plant designed for use of aluminum chloride-based catalyst.
Another process which has achieved significant commercial success is liquid phase alkylation for producing ethylbenzene from benzene and ethylene since it operates at a lower temperature than the vapor phase counterpart and hence tends to result in lower yields of by-products. For example, U.S. Pat. No. 4,891,458 (Innes) describes the liquid phase synthesis of ethylbenzene with zeolite Beta, whereas U.S. Pat. No. 5,334,795 (Chu) describes the use of MCM-22 in the liquid phase synthesis of ethylbenzene; and U.S. Pat. No. 7,649,122 (Clark) describes the use of MCM-22 in the liquid phase synthesis of ethylbenzene in the presence of a maintained water content. U.S. Pat. No. 4,459,426 (Inwood) describes the liquid phase synthesis of alkylbenzene with steam stabilized zeolite Y. U.S. Patent Publication No. 2009/0234169 A1 (Pelati) describes the liquid phase aromatic alkylation over at least one catalyst bed containing a first catalyst modified by inclusion of a rare earth metal ion.
Cumene has been produced commercially by the liquid phase alkylation of benzene with propylene over a Friedel-Craft catalyst, particularly solid phosphoric acid or aluminum chloride. Zeolite-based catalyst systems have been found to be more active and selective for propylation of benzene to cumene. For example, U.S. Pat. No. 4,992,606 (Kushnerick) describes the use of MCM-22 in the liquid phase alkylation of benzene with propylene.
Other Publications show use of catalysts comprising crystalline zeolites for conversion of feedstock comprising an alkylatable aromatic compound and an alkylating agent to alkylaromatic conversion product under at least partial liquid phase conversion conditions. These include U.S. 2005/0197517A1 (Cheng); U.S. 2002/0137977A1 (Hendrickson); and U.S. 2004/0138051A1 (Shan) showing use of a catalyst comprising a microporous zeolite embedded in a mesoporous support; WO 2006/002805 (Spano); and U.S. Pat. No. 6,376,730 (Jan) showing use of layered catalyst; EP 0847802B1; and U.S. Pat. No. 5,600,050 (Huang) showing use of catalyst comprising 30 to 70 wt. % H-Beta zeolite, 0.5 to 10 wt. % halogen, and the remainder alumina binder.
Other such Publications include U.S. Pat. No. 5,600,048 (Cheng) describing preparing ethylbenzene by liquid phase alkylation over acidic solid oxide such as MCM-22, MCM-49 and MCM-56, zeolite Beta, zeolite X, zeolite Y or mordenite; U.S. Pat. No. 7,411,101 (Chen) describing preparing ethylbenzene or cumene by liquid phase alkylation over acidic solid oxide such as PSH-3, ITQ-2, MCM-22, MCM-36, MCM-49, MCM-56, and zeolite Beta at conversion conditions including a temperature as high as 482° C. and pressure as high as 13,788 kPa; and U.S. Pat. No. 7,645,913 (Clark) describing preparing alkylaromatic compounds by liquid phase alkylation in a multistage reaction system over acidic solid oxide catalyst in the first reaction zone having more acid sites per unit volume of catalyst than the catalyst in the second reaction zone at conversion conditions including for ethylbenzene a temperature as high as 270° C. and pressure as high as 8,300 kPa, and for cumene a temperature as high as 250° C. and pressure as high as 5,000 kPa. U.S. Patent Publication No. 2008/0287720 A1 (Clark) describes alkylation of benzene over catalyst of MCM-22 family material in a reaction zone having water content maintained at from 1 to 900 wppm. U.S. Patent Publication No. 2009/0137855 A1 (Clark) describes a mixed phase process for producing alkylaromatic compounds from a dilute alkene feedstock which also includes alkane impurities. In the latter Publication, the volume ratio of liquid to vapor in the feedstock is from 0.1 to 10.
Existing alkylation processes for producing alkylaromatic compounds, for example, ethylbenzene and cumene, inherently produce polyalkylated species as well as the desired monoalkyated product. It is therefore normal to transalkylate the polyalkylated species with additional aromatic feed, for example benzene, to produce additional monoalkylated product, for example ethylbenzene or cumene, either by recycling the polyalkylated species to the alkylation reactor or, more frequently, by feeding the polyalkylated species to a separate transalkylation reactor. Examples of catalysts which have been used in the alkylation of aromatic species, such as alkylation of benzene with ethylene or propylene, and in the transalkylation of polyalkylated species, such as polyethylbenzenes and polyisopropylbenzenes, are listed in U.S. Pat. No. 5,557,024 (Cheng) and include MCM-49, MCM-22, PSH-3, SSZ-25, zeolite X, zeolite Y, zeolite Beta, acid dealuminized mordenite and TEA-mordenite. Transalkylation over a small crystal (<0.5 micron) form of TEA-mordenite is also disclosed in U.S. Pat. No. 6,984,764.
Where the alkylation step is performed in the liquid phase, it is also desirable to conduct the transalkylation step under liquid phase conditions. However, by operating at relatively low temperatures, liquid phase processes impose increased requirements on the catalyst, particularly in the transalkylation step where the bulky polyalkylated species must be converted to additional monoalkylated product without producing unwanted by-products. This has proven to be a significant problem in the case of cumene production where existing catalysts have either lacked the desired activity or have resulted in the production of significant quantities of by-products such as ethylbenzene and n-propylbenzene.
Although it is suggested in the art that catalysts for conversion of feedstock comprising an alkylatable aromatic compound and an alkylating agent to alkylaromatic conversion product under at least partial liquid phase conversion conditions are composed of a porous crystalline aluminosilicate molecular sieves having an MWW structure type, the present improved process has remained elusive. Finding a commercially acceptable catalyst for such processes conducted under at least partial liquid phase conversion conditions which increases conversion and does not significantly affect monoselectivity, i.e., lower di- or polyalkyl product make, would allow capacity expansion in existing plants and lower capital expense for grassroots plants as a result of lower aromatic compound/alkylating agent ratios. According to the present invention, it has now unexpectedly been found that a liquid phase or at least partial liquid phase alkylation process for producing alkylaromatics conducted in the presence of a specific catalyst comprising a porous crystalline material, e.g., a crystalline aluminosilicate, (“crystal”), having the structure type of FAU, *BEA or MWW, said catalyst having a Relative Activity measured as an RA220 (hereinafter more particularly described) of at least 7.5 or at least 8.6, for example from 7.5 to 30 or from 8.6 to 12.0, or an RA180 (hereinafter more particularly described) of at least 2.5 or at least 3.5, for example from 2.5 to 10 or from 3.5 to 6.0, yields a unique combination of activity and monoselectivity, while allowing operation at lower reaction pressures and lower alkylating agent feed supply pressures. This is especially the case when the process involves at least partial liquid phase alkylation for the manufacture of ethylbenzene or cumene. This eliminates the need for costly pressure booster compressors in the commercial plant, which is a tremendous commercial advantage.